Vinylidene olefin, which are branched monoolefins having the structure (R.sup.1)(R.sup.2)C.dbd.CH.sub.2 where R.sup.1 and R.sup.2 are alkyl groups, are of commercial importance as raw materials for use in producing-double tailed oxo alcohols and other functionalized derivatives, used in the manufacture of detergents, surfactants, specialty agricultural chemicals, and fuel or lubricant additives. Vinylidene olefins can be produced by dimerizing vinyl olefins.
U.S. Pat. No. 4,155,946 to Sato, Noguchi and Yasui discloses a process for dimerizing lower .alpha.-olefins in which the catalyst system is formed from (1) a trialkylaluminum compound, (2) a salt or complex of nickel, (3) a trivalent phosphorus compound selected from specified groups, and (4) a halogenated phenol.
U.S. Pat. No. 4,709,112 to Sato, Ikimi, Tojima and Takahashi describes a process for dimerizing lower .alpha.-olefins which uses a catalyst system formed from (1) a trialkylaluminum compound, (2) an organic salt or complex of nickel, (3) a trivalent phosphorus compound selected from specified groups, (4) a fluorinated isopropanol, and (5) a catalyst co-activator selected from specified types of halogenated compounds.
U.S. Pat. No. 4,973,788 to Lin, Nelson and Lanier describes a process for dimerizing a vinyl olefin monomer at a selectivity of at least 85 mol percent. This is accomplished by use of a catalyst which consists essentially of 0.001-0.04 mols of trialkylaluminum per mol of vinyl olefin, and conducting the reaction at a temperature in the range of about 100.degree.-140.degree. C. for a time sufficient to convert at least 80 mol percent of the initial vinyl olefin to a different product. The reaction rate under these conditions is quite slow, and thus a long reaction time is required. For example it is pointed out that the time required for 90 percent conversion at 120.degree. C. with 0.043 mols of aluminum alkyl catalyst per mol of initial vinyl olefin is about 94 hours, and that with 0.017 mols of the catalyst per mol of initial vinyl olefin the time required at 120.degree. C. is about 192 hours. It is also shown in the patent that although the reaction is faster at 172.degree. C. compared to 120.degree. C., the selectivity to vinylidene dimer is only 71 percent compared to 90 percent with the same catalyst concentration but at 120.degree. C.
In the presence of aluminum alkyl, vinyl olefins are dimerized to vinylidene olefins via the Markovnikov route. However a competing reaction which adversely affects yield of vinylidene olefin or the purity thereof is the dimerization to deep internal olefin dimer via the anti-Markovnikov route. Another undesirable competing reaction which normally tends to occur at dimerization temperatures the isomerization of vinyl olefin to internal isomer olefin via aluminum hydride route or by other known mechanisms. Such internal olefin formation adversely affects the dimer selectivity. It would be extremely desirable to suppress these competing reactions and be able to achieve high selectivity to vinylidene dimer in substantially shorter reaction periods than required in the process of U.S. Pat. No. 4,973,788 and without need for multicomponent catalyst systems such as described in U.S. Pat. Nos. 4,155,946 and 4,709,112.
The present invention has accomplished this goal.